ACMClassCourses · lillian039 · Jun 16, 2023 · Jun 16, 2023
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+## Linux and Unix and Android
+
+这三个架构之间的区别
+
+#### Linux Goals
+
+- Simplicity, elegance, consistency
+
+- Power and flexibility
+
+- Lack of useless redundancy
+
+#### Android – Design Goals
+
+- Open-source platform for mobile devices
+
+- Support 3rd party apps with robust, stable API
+
+- 3rd party apps compete on level playing field
+
+- Users need not deeply trust 3rd party apps
+
+- Support mobile user interaction
+
+- Manage app processes for users
+
+- Encourage apps to interoperate, collaborate
+
+- Full general-purpose OS
+
+<img src="1.jpg" alt="1" style="zoom:50%;" />
+
+<img src="2.jpg" alt="2" style="zoom:50%;" />
+
+<img src="E:\Tencent\WeChat Files\WeChat Files\wxid_ia5hjahervpp11\FileStorage\Temp\1686907384593.jpg" alt="1686907384593" style="zoom:50%;" />
+
+<img src="D:\a_homework_of_c++\2_2_semester\os-2023-notes\W13D2\4.jpg" alt="4" style="zoom:50%;" />
+
+![3](D:\a_homework_of_c++\2_2_semester\os-2023-notes\W13D2\3.jpg)
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+### File systems
+
+#### Part 1 Review
+
+- Memory Manager（Review）
+
+  - Physical Memory ( no abstract )
+
+  - Virtual Memory
+
+    - Process : VM_area_struct (linear)
+
+    - mmap ( vaddr, __ , __ , file , off , size )
+
+      if ( vaddr = 0) anywhere
+
+      file = fd(file back ) / file = -1 anonymous
+
+      <img src="2.png" alt="2" style="zoom:50%;" />
+
+    - phy : Buddy
+
+- File = { a set of Bytes }
+
+- FileSystem = { a set of files }
+
+#### Part 2 Setjmp / Longjmp ( long goto )
+
+```c++
+main(){
+	e = setjump(jx)
+	swtich (v)...//ai
+	bar();
+}
+bar(){
+	foo();
+}
+foo(){
+	if(something erro) long_jump (jx,value)//value tell what happens
+}
+```
+
+`jx` 栈结构 记录下跳转时 `set jump` 所处的所有状态
+
+| ai   | stack in main |
+| ---- | ------------- |
+
+<img src="1.png" alt="2" style="zoom:50%;" />
+
+#### Part 3 File System
+
+File Systems = { a set of files }
+
+- Insert / Delete / Searching
+
+Question:
+
+- How do you find information
+- How do you keep one user from reading another user's data?
+- How do you know which blocks are free?
+
+magic number： D0,CF,11,E3...
+
+**MZ：**DOS MZ executable
+
+该文件可以通过文件开头的ASCII字符串“MZ”（十六进制：4D 5A）来识别（“幻数”）。 “MZ”是Mark Zbikowski 的缩写，Mark Zbikowski是MS-DOS的主要开发者之一。
+
+**ELF ：**Executable and Loadable Format
+
+ELF文件由4部分组成，分别是ELF头（ELF header）、程序头表（Program header table）、节（Section）和节头表（Section header table）。
+
+<img src="4.png" alt="2" style="zoom:50%;" />
+
+文件中：section
+
+内存中：segment
+
+<img src="3.png" alt="2" style="zoom:50%;" />
+
+文件和目录都是文件
+
+<img src="5.png" alt="2" style="zoom:50%;" />
+
+mount（挂载）：
+
+mount 命令用于将某些设备上的文件系统附加到大文件树，加载文件系统到指定的加载点。相反，umount 命令将再次将其分离。此命令最常用于挂载cdrom，使我们可以访问cdrom中的数据
+
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+### I / O
+
+- **Q1: How to drive an I / O (or device)** （Today's topic）
+- Q2: How to Read / Write
+
+Challenges for OS
+
+- For reasons... DMA, Interpretation
+
+  DMA ：全称Direct Memory Access，即直接存储器访问。
+
+- Variety of Devices
+
+Sequence vs Random
+
+#### I / O devices
+
+NFC Field
+
+Field Bus：
+
+- CAN：控制器局域网络（Controller Area Network）
+- LONWORKS：Lonworks代表本地运营网络。
+
+USB 本身是个网络
+
+#### Directed Memory Access
+
+同步方式：阻塞式
+
+异步方式：IO 太慢了，通常采用异步，即非阻塞
+
+![1](1.jpg)
+
+低端 DMA：
+
+DMA 发出 `add I/O` 指令，将数据存在自己的 `buffer` 里头，再发出 `add Memory` 指令，将自己 `buffer` 中的数据存入 `Main Memory`，两次总线访问。
+
+高端 DMA：**On fly：**
+
+DMA 发出 `add I/O` 指令，再发出 `add Memory` 指令，直接将数据传入 `Main Memory`，一次总线访问。
+
+#### Interrupts Revisited
+
+要先 `request` 中断线
+
+#### Precise Interrupt
+
+Four properties of a precise interrupt:
+
+- The PC saved in a known place.
+- All instructions before that pointed to by PC have fully executed.
+- No instruction beyond that pointed to by PC has been executed.
+- Execution state of instruction pointed to by PC is known.
+
+
+
+task struct $\to$ files $\to$ file struct
+
+- top-half
+- bottom-half
+
+DMA：
+
+request irq  dma：使用 request_irq () 函数来注册中断服务函数
+
+register block (or char)
+
+H / W（HardWare）
+
+Ref：LDD（Linux Device Driver）
+
+
+
+#### Goals of the I/O Software
+
+Issues:
+
+- Device independence
+- Uniform naming
+- Error handling
+- Synchronous versus asynchronous
+- Buffering.